Much of our knowledge concerning the physiologic significance of various hormones is extrapolated from changes obtained following administration of the hormone to the animal or isolated preparation. The availability of sensitive methods for the detection of circulating polypeptide and steroid hormones afford an opportunity to investigate the validity of the presumed interrelationship. The concentration of various hormones, such as growth hormone, ACTH and insulin will be monitored in the plasma of conscious dogs under a variety of conditions designed to evoke changes in their secretion. Concomitantly, measurement will be made of rates of production and utilization of endogenous glucose, free fatty acids, glycerol. Appropriate pharmacologic agents, such as precursors and blocking agents, will be used to alter hormonal secretion and/or metabolic responses in order to gain more insight into the mechanism of the hormonal-metabolic interrelationship.